U.S. patent application number 10/157683 was filed with the patent office on 2003-12-04 for method for plasma etching a wafer after backside grinding.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Chang, Feng-Ru, Chang, Yeong-Rong, Lu, Gau-Ming.
Application Number | 20030224583 10/157683 |
Document ID | / |
Family ID | 29582527 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030224583 |
Kind Code |
A1 |
Chang, Feng-Ru ; et
al. |
December 4, 2003 |
Method for plasma etching a wafer after backside grinding
Abstract
A method for plasma etching a wafer after a backside grinding
process which incorporates an oxidation pretreatment step is
disclosed. The method includes the step of first grinding a
backside of a wafer to expose a bare silicon surface. The bare
silicon surface is then oxidized in an oxidation chamber to form a
substantially uniform silicon oxide layer of at least 50 .ANG.
thick, and preferably at least 100 .ANG. thick. The wafer is then
positioned in a plasma etch chamber with an active surface of the
wafer exposed, and a surface layer etched away by an oxygen plasma
without causing any further silicon oxide formation on the backside
of the wafer. The present invention novel plasma etching method can
be advantageously used for removing an organic material layer, such
as a photoresist layer from a wafer surface.
Inventors: |
Chang, Feng-Ru; (Tainan,
TW) ; Lu, Gau-Ming; (Taipei, TW) ; Chang,
Yeong-Rong; (Tainan, TW) |
Correspondence
Address: |
TUNG & ASSOCIATES
Suite 120
838 W. Long Lake Road
Bloomfield Hills
MI
48302
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
|
Family ID: |
29582527 |
Appl. No.: |
10/157683 |
Filed: |
May 29, 2002 |
Current U.S.
Class: |
438/459 ;
438/710 |
Current CPC
Class: |
H01L 21/02054
20130101 |
Class at
Publication: |
438/459 ;
438/710 |
International
Class: |
H01L 021/461; H01L
021/46; H01L 021/30; H01L 021/302 |
Claims
What is claimed is:
1. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pre-treatment step comprising the steps
of: grinding a backside of a wafer exposing a bare silicon surface;
oxidizing said bare silicon surface forming a silicon oxide layer
of at least 50 .ANG. thick in an oxidation chamber; positioning
said wafer in a plasma etch chamber with an active surface of the
wafer exposed; and plasma etching away a surface layer from said
active surface of the wafer.
2. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of wet stripping a residual surface
layer away from said active surface of the wafer.
3. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of wet stripping a residual surface
layer away by exposing said active surface of the wafer to a
diluted acid solution.
4. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of grinding said backside of the wafer
in a backside lapping process.
5. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of oxidizing said bare silicon surface
in an oxidation furnace.
6. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of oxidizing said bare silicon surface
in an oxidation furnace for a time period between about 30 min. and
about 100 min.
7. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of plasma etching away a surface layer
by exposing said wafer to an oxygen plasma.
8. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of plasma etching away a photoresist
coating layer by oxygen plasma in a plasma ashing process.
9. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of: plasma etching away a photoresist
coating layer by oxygen plasma; and wet stripping any residual
photoresist coating layer from said wafer.
10. A method for plasma etching a wafer after backside grinding
incorporating an oxidation pretreatment step according to claim 1
further comprising the step of plasma etching away an organic
material layer by oxygen plasma in a plasma etching process.
11. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
comprising the steps of: grinding a backside of a wafer exposing a
bare silicon surface; oxidizing said bare silicon surface forming a
silicon oxide layer of at least 50 .ANG. thick in an oxidation
chamber; positioning said wafer in a plasma etch chamber with an
active surface of the wafer exposed; plasma etching away said
photoresist layer on said active surface of the wafer; and wet
stripping away any residual photoresist layer by a wet bench
process.
12. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of stripping said
residual photoresist layer away by a wet bench process that
utilizes a diluted acid stripper.
13. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of oxidizing said
bare silicon surface until a SiO.sub.2 layer having a thickness
between about 50 .ANG. and about 200 .ANG. is formed.
14. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of oxidizing said
bare silicon surface for a time period between about 30 min. and
about 100 min.
15. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away said photoresist layer by an oxygen plasma.
16. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away a photoresist layer formed of a polymeric material.
17. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away a photoresist layer formed of an organic material.
18. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away a photoresist layer formed of polyimide.
19. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away a photoresist layer at an etch rate of at least 50K
.ANG./min.
20. A method for preventing wafer backside non-uniform oxidation
during a plasma ashing process for removing a photoresist layer
according to claim 11 further comprising the step of plasma etching
away a photoresist layer for a time period of at least 30 sec. at
an etch rate of at least 50K .ANG./min.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to a method for
plasma etching a wafer surface for removing an unwanted coating
layer and more particularly, relates to a method for plasma etching
a photoresist layer from a wafer surface after a backside grinding
of the wafer is performed without the non-uniform oxide layer
formation defects.
BACKGROUND OF THE INVENTION
[0002] In the fabrication of semiconductor devices, various
processing steps are started with a photolithographic process to
first define a circuit on the wafer. For instance, in a modern
memory device, multiple layers of metal conductors are required for
providing a multi-layer metal interconnect structure. As the number
of layers of metal interconnects increase, while the device
geometry continuously decreases to allow more densely packed
circuits, the photolithographic process required to define patterns
of circuits becomes more complicated and difficult to carry
out.
[0003] After a process for forming metal vias or lines in an
insulating layer is completed, a photoresist layer must be
stripped. As a result, it is necessary to subject the wafer to a
wet etching process for removing the photoresist layer. For
instance, a wet stripping process can be implemented after a
photoresist dry stripping process by utilizing a wet etchant such
as ACT.RTM. 690C or EKC.RTM. 265 in order to remove the photoresist
layers. The ACT.RTM. 690C is a mixture of DMSO
(dimethyl-sulphur-oxide), MEA (mono-ethyl-amine) and catechol,
while EKC.RTM. 265 is a mixture containing HDA (hydroxy-amine). The
conventional wet dip process requires a special buffer solvent
treatment step in order to avoid or minimize metal corrosion
problems in the circuits already formed on the wafer surface.
[0004] Wet etching is the more frequently used technique for
stripping photoresist films from silicon wafers where the complete
removal of resist images without adversely affecting the wafer
surface is desired. The resist layer or images should be completely
removed without leaving any residues, including contaminant
particles that may have been present in the resist. The underlying
surface of the photoresist layer should not be adversely affected,
for instance, accidental etching of the metal or oxide surface
should be avoided. Liquid etchant strippers should produce a
reasonable yield in order to prevent redeposition of dissolved
resist on the wafers. The etchant should completely dissolve the
photoresist layer in a chemical reaction, and not just lifting or
peeling so as to prevent redeposition. It is also desirable that
the etching or stripping time be reasonably short in order to
permit high wafer throughput.
[0005] Other wet etchants such as sulfuric acid (H.sub.2SO.sub.4)
and mixture of H.sub.2SO.sub.4 with other oxidizing agents such as
hydrogen peroxide (H.sub.2O.sub.2) may also be used in stripping
photoresist or in cleaning a wafer surface after the photoresist
has been stripped by other means. For instance, a mixture may be
seven parts H.sub.2SO.sub.4 to three parts 30% H.sub.2O.sub.2, or a
mixture of 88% sulfuric acid and 12% nitric acid. Wafers to be
stripped can be immersed in the mixture at a temperature between
about 100.degree. C. and about 150.degree. C. for 5.about.10
minutes and then subjected to a thorough rinse of deionized water
and dried in dry nitrogen. This type of inorganic resist strippers,
such as the sulfuric acid mixtures, is very effective in the
residual-free removal of highly post-baked resist. They are more
effective than organic strippers and the longer the immersion time,
a cleaner and more residue-free wafer surface can be obtained.
[0006] The photoresist dry stripping process is normally carried
out by a plasma etching or sometime known as a "plasma ashing"
process which is effective in ashing organic photoresist layers.
The plasma ashing process is an isotropic etch process for organic
photoresist in an oxygen glow discharge where atomic oxygen is
produced. Oxygen atoms react with organic photoresist material to
form volatile products such as CO, CO.sub.2 and H.sub.2O. A
barrel-type reactor is frequently used for the plasma ashing
processing. For instance, a batch of wafers such as 25 wafers
coated with 1 .mu.m photoresist layer can be processed in less than
10 min.
[0007] When the plasma ashing method is used to remove photoresist
layers on a wafer surface, the wafer is frequently ground on the
backside and therefore, a bare silicon surface is exposed when the
wafer is loaded into the plasma etch chamber. During the oxygen
plasma ashing process, not only the top side of the wafer is
etched, the peripheral edge of the backside of the wafer is also
attacked by the oxygen plasma. As a result, a sawtooth shaped
pattern of silicon oxide is formed along the peripheral edge of the
wafer on the backside. This is shown in FIG. 1. For wafer 30, a
sawtooth shaped peripheral area 32 where the bare silicon exposed
by the backside grinding process is oxidized by the oxygen plasma
forming silicon oxide. The surface oxidation of the bare silicon is
mainly caused by oxygen plasma that flows into the shallow trench
lines 34 that are provided on the surface of the heater plate in
the plasma etcher for holding the wafer. At near the three ejector
pin holes 36, the oxygen plasma also tend to leak in and cause
oxidation of the bare silicon surface near the holes. The silicon
oxide layer formed along the peripheral edge of the wafer backside
makes the backside surface uneven and furthermore, the thickness of
the wafer uneven. Such uneven thickness of the wafer may cause
additional stress problems. When another backside grinding process
is attempted to even out the backside surface, the wafer may break
during the grinding process and cause a catastrophic loss.
[0008] It is therefore an object of the present invention to
provide a method for plasma etching a wafer after a backside
grinding process that does not have the drawbacks or shortcomings
of the conventional plasma etching method.
[0009] It is another object of the present invention to provide a
method for plasma etching a wafer after a backside grinding process
exposing a bare silicon surface that does not oxidize the backside
of the wafer.
[0010] It is a further object of the present invention to provide a
method for plasma etching a wafer after a backside grinding process
that does not cause the formation of silicon oxide on the backside
of the wafer.
[0011] It is another further object of the present invention to
provide a method for plasma etching a wafer after a backside
grinding process by first oxidizing the wafer before the plasma
etching process is carried out.
[0012] It is still another object of the present invention to
provide a method for plasma etching a wafer after a backside
grinding process by first placing the wafer in an oxidation furnace
for growing a uniform layer of silicon oxide on the backside of the
wafer prior to the plasma etching process.
[0013] It is yet another object of the present invention to provide
a method for plasma etching a wafer after a backside grinding
process by first growing a silicon oxide layer that is at least 50
.ANG. thick on the backside of the wafer.
[0014] It is still another further object of the present invention
to provide a method for plasma etching a photoresist layer on a
wafer after a backside grinding process is conducted wherein the
oxygen plasma does not form a silicon oxide layer on the backside
of the wafer.
SUMMARY OF THE INVENTION
[0015] In accordance with the present invention, a method for
plasma etching a wafer after a backside grinding process without
forming uneven silicon oxide layer on the backside along a
peripheral edge is disclosed.
[0016] In a preferred embodiment, a method for plasma etching a
wafer after a backside grinding process which incorporates an
oxidation pre-treatment step can be carried out by first grinding a
backside of the wafer exposing a bare silicon surface; oxidizing
the bare silicon surface forming a silicon oxide layer of at least
50 .ANG. thick in an oxidation chamber; positioning the wafer in a
plasma etch chamber with an active surface of the wafer exposed;
and plasma etching away a surface layer from the active surface of
the wafer.
[0017] The method for plasma etching a wafer after backside
grinding may further include the step of wet stripping a residual
surface layer away from the active surface of the wafer, or the
step of wet stripping a residual surface layer away by exposing the
active surface of the wafer to a diluted acid solution. The method
may further include the step of grinding the backside of the wafer
in a backside lapping process. The method may further include the
step of oxidizing the bare silicon surface in an oxidation furnace,
or the step of oxidizing the bare silicon surface in an oxidation
furnace for a time period between about 30 min. and about 100 min.
The method may further include the step of plasma etching away a
surface layer by exposing the wafer to an oxygen plasma, or the
step of plasma etching away a photoresist coating layer by oxygen
plasma in a plasma ashing process. The method may further include
the steps of plasma etching away a photoresist coating layer by an
oxygen plasma and wet stripping any residual photoresist coating
layer from the wafer. The method may further include the step of
plasma etching away an organic material layer by an oxygen plasma
in a plasma etching process.
[0018] The present invention is further directed to a method for
preventing wafer backside non-uniform oxidation during a plasma
ashing process for removing a photoresist layer which can be
carried out by the steps of grinding a backside of a wafer exposing
a bare silicon surface; oxidizing the bare silicon surface forming
a silicon oxide layer of at least 50 .ANG. thick in an oxidation
chamber; positioning the wafer in a plasma etch chamber with an
active surface of the wafer exposed; plasma etching away the
photoresist layer on the active surface of the wafer; and wet
stripping away any residual photoresist layer by a wet bench
process.
[0019] The method for preventing wafer backside non-uniform
oxidation during a plasma ashing process for removing a photoresist
layer may further include the step of stripping the residual
photoresist layer away by a wet bench process that utilizes a
diluted acid stripper, or the step of oxidizing the bare silicon
surface until a SiO.sub.2 layer that has a thickness between about
50 .ANG. and about 200 .ANG. is formed. The method may further
include the step of oxidizing the bare silicon surface for a time
period between about 30 min. and about 100 min., or the step of
plasma etching away the photoresist layer by an oxygen plasma, or
the step of plasma etching away a photoresist layer formed of a
polymeric material, or the step of plasma etching away a
photoresist layer formed of an organic material, or the step of
plasma etching away a photoresist layer formed of polyimide. The
method may further include the step of plasma etching away a
photoresist layer at an etch rate of at least 50,000 .ANG./min. The
method may further include the step of plasma etching away a
photoresist layer for a time period of at least 30 sec. at an etch
rate of at least 50,000 .ANG./min.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] These and other objects, features and advantages of the
present invention will become apparent from the following detailed
description and the appended drawings in which:
[0021] FIG. 1 is a plane view of a backside of a wafer after a
conventional plasma etching process is conducted on bare silicon
exposed by a backside grinding process.
[0022] FIG. 2 is a process flow chart of the present invention
method.
[0023] FIG. 3 is a process flow diagram of the present invention
wet bench process after the plasma ashing step is carried out.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The present invention discloses a method for plasma etching
a wafer after a backside grinding process is conducted that
incorporates an oxidation pre-treatment step such that non-uniform
formation of silicon oxide on the backside from the bare silicon
can be avoided.
[0025] In the present invention novel method, a backside of a wafer
is first ground to expose a bare silicon surface. The bare silicon
surface is then oxidized to form a silicon oxide layer of at least
50 .ANG. thick in an oxidation chamber. The wafer is then
positioned in a plasma etch chamber with an active surface of the
wafer exposed such that a surface layer can be plasma etched away
from the active surface of the wafer. Optionally, the present
invention method further includes the step of wet stripping in a
wet bench process a residual surface layer away from the active
surface of the wafer.
[0026] The oxidation step for oxidizing the bare silicon surface on
the wafer backside can be carried out in an oxidation furnace for a
time period between about 30 min. and about 100 min., such that a
silicon oxide layer of at least 50 .ANG. thick can be uniformly
formed on the wafer backside surface.
[0027] The present invention further discloses a method for
preventing wafer backside non-uniform oxidation during a plasma
ashing process for removing a photoresist layer which can be
carried out by first grinding a backside of a wafer to expose a
bare silicon surface; then oxidizing the bare silicon surface to
form a silicon oxide layer of at least 50 .ANG. thick in an
oxidation chamber; then positioning the wafer in a plasma etch
chamber with an active surface of the wafer exposed; then plasma
etching away the photoresist layer on the active surface of the
wafer; and wet stripping away any residual photoresist layer by a
wet bench process.
[0028] Referring now to FIG. 2, wherein a process flow chart 40 of
the present invention method for plasma etching a wafer after a
backside grinding process incorporating an oxidation pretreatment
is shown. It is seen that in the first step 42 of the process, a
backside of a wafer is ground to expose a bare silicon surface. The
wafer with the bare silicon surface on the backside is then
oxidized in an oxidation furnace for a suitable time period, i.e.
for a time period between about 30 min. and about 100 min., such
that a silicon oxide layer of at least 50 .ANG. thick, or
preferably at least 100 .ANG. thick is formed. The formation of the
substantially uniform layer of silicon oxide in step 44 from the
bare silicon surface substantially prevents any further silicon
oxide growth when the wafer is later subjected to oxygen plasma in
the plasma ashing step 46 shown in FIG. 2.
[0029] The plasma ashing step can be carried out with an oxygen
plasma to etch away a front side, i.e. an active side of the wafer
to remove a surface layer, such as a photoresist layer or any other
organic material layer. When the oxygen plasma is utilized, a
desirable etch rate of about 65,000 .ANG./min. can be realized. For
a photoresist layer of normal thickness, a total plasma etching
time required is between about 30 sec. and about 60 sec. The word
"about" used in this writing indicates a range of values that are
.+-.10% of the average value given. It should be emphasized that
the formation of the thin layer of silicon oxide uniformly on the
backside of the wafer, i.e. in step 44, substantially prevents the
further growth or formation of silicon oxide and particularly the
formation of non-uniform thickness of silicon oxide on the backside
of the wafer during the plasma ashing step 46. The defect of
saw-tooth patterned formation of silicon oxide, shown in FIG. 1, on
a bare silicon surface along a peripheral edge of the wafer
backside can therefore be avoided.
[0030] After the completion of the plasma ashing step 46, the wafer
can be further cleaned to complete the photoresist removal process
in a wet bench process 48.
[0031] The wet bench step 48 can be shown in a process flow diagram
in FIG. 3. A wafer 12 after the plasma ashing process for removing
most of the photoresist layer is first dipped into an etch tank
containing ACT.RTM. etch solution in bath 14 for conducting a first
etch reaction. The composition of ACT.RTM. is a mixture of
dimethyl-sulphur-oxide, mono-ethyl-amine and catechol. The ACT.RTM.
solution is normally maintained at a temperature higher than room
temperature, for instance, at a temperature of at least 60.degree.
C. After a suitable time period of immersing in the first bath 14,
the wafer 12 is removed to the second ACT.RTM. bath 16 and again
immersed for a suitable length of time. The wafer 12 is then
immersed in a buffer solvent bath 18 to substantially neutralize
the residual acid solution on the wafer surface. The buffer solvent
bath 18 may contain a solvent such as isopropyl alcohol or an NMP.
The wafer 12 is immersed in the buffer solvent for a sufficient
length of time so as to neutralize all residual acid on the wafer
surface, for instance, a sufficient length of time is at least 10
min. The wafer 12 is then moved to a quick dump rinse tank 20 for a
rinse operation by deionized water, which is then followed by a
final rinse step carried out in bath 22 with deionized water. After
the wafer 12 is thoroughly rinsed, it is dried in a drying tank 24
such as a Maragoni tank that utilizes isopropyl alcohol vapor for
drying.
[0032] The present invention novel method for plasma etching a
wafer after a backside grinding process which incorporates an
oxidation pretreatment step has therefore been amply described in
the above description and in the appended drawings of FIGS. 2 and
3.
[0033] While the present invention has been described in an
illustrative manner, it should be understood that the terminology
used is intended to be in a nature of words of description rather
than of limitation.
[0034] Furthermore, while the present invention has been described
in terms of a preferred embodiment, it is to be appreciated that
those skilled in the art will readily apply these teachings to
other possible variations of the inventions.
[0035] The embodiment of the invention in which an exclusive
property or privilege is claimed are defined as follows.
* * * * *